The initiation of parturition is caused by the interaction of various hormonal stimuli. Their precise mode of action on the cellular and subcellular level is largely unknown. Prostaglandin F2 alpha appears to be the final activator of the uterus. Since calcium is required for contraction, in muscle systems, we hypothesize that hormones such as prostaglandins (PG) and oxytocin exert their effect through regulation of subcellular calcium transport, and we have shown such effects in vitro during the previous period of this research grant. We plan to purify and characterize the subcellular organelles, enzymes and proteins involved in myometrial calcium transport, isolate model systems and study their interactions. Characteristic enzyme activities will be used to follow the course of purification of sarcoplasmic reticulum (SR) and of cell membrane. ATP-dependent calcium binding will be studied in SR, cell membrane and mitochondria. Calcium binding proteins from sarcoplasmic reticulum and cell membrane, and Ca-activated ATPase will be isolated and charecterized using chromatography and electrophoresis.